Tandem testing of telephone lines



April 14, 1970 w. CHULAK TANDEM TESTING OF TELEPHONE LINES April 14, 1970 filed Jan. 22. 1968 W. CHULAK TANDEM TESTING OF TELEPHONE LINES ,5 Sheets-Sheet 2 MIM .5 Sheets-Sheet 3 /NVENTR W. CHULAK |O mm @E m mz x ml n x v x x m m @-z x t l j x x x Tm Q L m m Tm W. CHULAK TANDEM TESTING OF TELEPHONE LINES mnm April 14, 1970 Filed Jan. 22. 1968 April 14, 1970 w. cHULAK TANDEM TESTING OF' TELEPHONE LINES Filed Jan. 22. 1968 .5 Sheets-Sheet 4 /NVEA/rof? w.cHuLAK AGENTS April 14, 1970 w. cHULAK 3,506,794

TANDEM TESTING 0F TELEPHONE LINES Y Filed Jan. 22. 1968 .5 Sheets-Sheet 5 @7a/@cam Uni@ Sete Patent f 3,506,794 v .,TANDEM TESTING OF TELEPHONE LINES William Chulak, Chambly, Quebec, Canada, assignor to Northern Electric Company Limited, Montreal, Quebec,

Canada Filed Jan. 22, 1968, Ser. No. 699,561 Int. Cl. H04m 3/26 U.S. Cl. 179-175.2 5 Claims ABSTRACT THE DISCLOSURE This invention relates to tandem testing of telephone offices located within a limited distance from a remote oflice equipped for remote testing. Such testing is carried out under4 the control of a test desk located at a test center, through, the remotely controlled ofce, and over a direct current trunk between the remotely controlled oflice and the other oilice located within a limited distance of the remotely controlled oice.

This invention relates to remote testing of subscriber telephone lines and more particularly to tandem testing of offices located within a limited distance from a remote oice equipped for remote testing.

To ensure a high standard of telephone service, telephone lines must be tested regularly. Local test desks are usually provided in test centers for providing the necessary tests. Until recently, most of the testing was done using ai dedicated direct current trunk between the test center and each of the various test trunk circuits in the office being tested. The operating range of the relays used, however, limits the length of these test trunks. Lately, remote testing circuits have been developed that eliminate the distance limitations between the test center and the tested offices. These circuits provide essentially a remotely controlled version of the test desk in each oliice tested. The remote test circuit is controlled by the regular test keys at the test ldesk using alternating current signals transmitted over a voice-frequency test path. The test results are returned to the test desk by supervisory and telemetry signals over the same test path. p

However, in areas where there are plural `offices within a limited distance, it would be more economical to test such oices through a single remote office equipped with the remote testing equipment. Tandem testing of plural ofiices through a single ollice equippedwith the remote testing equipment would eliminate the need of providing the costly remote testing equipment for each remote oice.

It is, therefore, the main feature of the present invention to allow tandem testing of a plurality of offices located within a predetermined distance from a remotely controlled otiice through the remote office. Such testing is carried out under control of the test desk over a direct current trunk between the remotely controlled oiiice and the other oiices.

The invention will now be described with references to the accompanying `drawings in which:

FIG. 1 illustrates a block diagram of a known remote testing system; p

FIG. 2. illustrates in a block diagram form the addi- 3,506,794 Patented Apr. 14, 19.70

ICC

tional circuitry required for providing tandem testing in accordance with the invention;

FIG. 3 illustrates additions to the known test desk and local testing circuit for providing tandem testing;

FIG. 4 illustrates a receiver circuit of the type used in the known testing system;

FIG. 5 illustrates a relay circuit for transferring the T, R, S leads from the Test Distributor Control Circuit of the remotely controlled office to one of the other offices in the area;

FIG. 6 illustrates the additions to the common remotely controlled oice for providing tandem testing; and

FIG. 7 illustrates the Test Distributor Control Circuit of one of the other otlices to be tested.

Referring to FIG. 1, there is shown a general block diagram of a known subscriber loop remote testing system. Generally speaking, the remote testing system is controlled by regular test keys at a test desk 10` using A.C. signals transmitted over a voice frequency test path 11. Test results are returned to the test desk by supervisory and telemetry signals over the same test path. The path can ibe a dedicated trunk, or more economically, it can be a nondedicated circuit dialed up through the regular telephone switching system.

To test a line in a remote ooe, the tester first establishes a connection from the test desk 10 to the remote testing circuit in the distant oilice. If a nondedicated trunk is used, the tester dials a connection to the remote oice over an activation path 12 comprising subscriber line circuits 13 and 14 and switching equipments 15 and 16. This activates test trunk 17 at the remote olice where a connection is automatically dialed over subscriber line circuits 18 and 19 from the remote testing circuit 20 to the test desk 10. The tester breaks the rst connection over the activation path 12 and then conducts all testing over the test path 11. When the test path has been setup, the tester, completes the connection by plugging the test cord into the test jack of test trunk 21.

If a dedicated test path is used, the tester simply plugs a test cord into the test jacket of test trunk 21. The remote oice test trunk 17 and activation path 12 are omitted.

The tester then selects a Test Distributor Control Circuit, a Regular Incoming Test Trunk, a No-Test Incoming Test Trunk, a Main Distributing Frame rI est Trunk or a Test Trunk and Selector Circuit depending upon the type of office being tested and the kind of testing to be done. He makes the :connection to the desired customer line in the normal manner by key pulsing or dialing. Remote testing circuits 22 translate these key operations into multifrequency control signals called order codes, consisting of various combinations of 3 out of 14 audio frequencies. The multifrequency control signals are transmitted to the remote office each time a key is koperated and released. At the remote testing circuiti 20, the multifrequency control signals are received and decoded to set up the appropriate test connections ,toY Test Trunks 23 through 26. v

The D.C. current measurements made at the remotely controlled olce are translated to frequency modulated waves and transmittedback via test path 411 to testing circuits 22 at the test center. There theFM signals are .demodulated and. the resul ..3 Y `ting vdirect. current signals are measured.

The above is a brief description of a known remote testing circuit, a more detailed description of which may be found in the December 1966 issue of the Bell Laboratories Record.

FIG. 2 illustrates in a block diagram form the additional circuitry required for testing several offices within a limited distance from a regular remotely controlled oice. Generally speaking, when the tester has established a connection between the local test desk and the remotely controlled office, a connection may be established lto .a tandemtest circuitu27, by. operating avspecial keyat the local test desk. The tester. can. then proceed to dial the subscribernumberrin preparation to testout -the subscriber line andf/or telephone set., During the course of his testing, the test man' may test a Regular or Notest Trunk 28, aV MDF Trunk 29 orga Test Trunk and Selector Circuit 30 by voperating the associated keys at the local test desk. y l I s In FIG. 3, there are shown additions to be made to the conventional test desk 10 to provide the required keys TN for tandem testing, and to the local testing circuits 22 for providing the additional start relays ST forv making the proper connections to the multitone generator which causes the appropriate order codes to be transmitted.,The circuits are identical to the ones provided for the regular remote testing system and are shown schematically. A more detailed description thereof may be found in the above-identified Bell Laboratories Record at pages 371- 374. There are tive TN keys and `tive ST relays illustrated for providing tandem testing to five ofiices within alimited distance from the remotely controlled ofce. However, if there are more oices, more circuits may be added. The operation of any one of the keys 'TN-1 to TN-S operates its corresponding relay ST-1 to ST-S to start the appropriate multifrequency generator to send the order codes to the test path.

The order codes transmitted over test path 11 are received by a multifrequency receiver illustrated schematically in FIG. 4. A more detailed description of the receiver may be found in the above-identified Bell Laboratories Record at page 373. A cut apart filter 31 divides the order codes into three groups corresponding to the three frequencies generated by the multifrequency code generator. E'ach of these groups of frequencies is applied toa detector 32, 33 or 34 which detect the A, B or C frequencies. Each of these detectors is sharply tuned to the. corresponding frequency and provides an output only when a signal of that frequency with a substantial amplitude appears at its input. The outputs of detectors A, B or. C operate corresponding relays A13-A4,v B0-B4 OI' C0-C4.

.FIG. 5 villustrates relays TN-l to TN-S whichare operated when the corresponding keysat the local test desk are operatedvand relays TNR-1 to TNR-5 which are operated when the keys TNA to TN-Sare released. Each of the .relays TN-vl to TN-S and TNR-1 to TNR-5 are operated in response to Ithe simultaneous operation of one .relay from each group of relays AIV-A4, B0-B4 and C0-C4. In other words, each of relays 'TN-1 Vto TN-4 andTNR-l to TNR-4v responds to a unique combination of. A, -B and C relays. Moreover, each of the operate relays TNfl to .'IN-4locks through a break contact of release relays TNR-1 to TNR-5.

The operation of one of relays TN-1 to TN-S close corresponding contacts TN-1 to TN-S in FIG. 6 to trans.-v fer the T, R, S leadfsfrom the Test Distributor Control Circuit in the remotely controlled'ofiice: to the TestDistributor Control Circuit in one of the other offices -to be testedfThe' tester'ca'n now proceed to dial the subscriber number'inpreparation to test out the subscriber line and/ or telephone set.'

During the course -of 'his testing,l the' tester may find that he will have to test a Touch Tone feature, a MDF 4 l TestI'runk and/or a Test Trunk and Selector Circuit for example. All these tests can be performed by operating associated keys TT, MDF or TS respectively at the local test desk. These keys will operate start relays to energize corresponding multifrequency generators to send appropriate frequencies over the test path to the remotely controlled oice and eventually operate contacts TT, MDF or TS shown in FIG. 61.

The closure of contacts TT places a direct ground on supervisory lead TN to the oice under test through normally closed contacts MDF and TS as illustrated in FIG. 6. The direct ground on supervisory lead TN operates relay T and marginal relays TA and TC in FIG. 7. The operation of relaysT, TA and TC closes contacts T-LiTA-l andTCl4 to operate relaysTE, and TD. The leriergization of relays TE, TB and TDyoperate contacts"TE'-1', TB-l and TD1 to complete a circuit to the Regular or No-test Trunk and to test the Touch Tone Feature thereof by closing contacts TD-Z.

. The Aclosure of contacts MDI-""places low resistance ground through resistor RL on supervisory lead TN to the Tandem Oice through normally closed contacts TS to operate relay T and marginal relay TA. The operationof rrelays T and TAA close contacts T-l and TA-l lto operate relays TE and TB. The 'e'nergization of relays TE and TB operates contacts vTE-.l'and TB-l to com plete a current to the MDF trunk.V

The closure of contacts TS applies vhigh resistance ground through Yresistor R4`to supervisory lead TN and operates relay T alone. The 'operation of relay T closes contacts T-'1 and operatesrelay TE. The operation of relay TE completes a circuit to the Test Trunk and Selector Circuit.

On completion of testing the TN key under operation is releasedand the corresponding TNR relay, FIG. 5, is energized as mentioned previously. The operation of the corresponding relay TNR releasesthe operated TN relay and operates relay D, FIG. 6 which in turn operates relay D1. The operation of relay D1 will replace the usual high resistance ground'on the sleeve'S of the trunk under Iuse'with a lower resistance ground throughfre sistor RL1. The lower resistance ground on the sleeve S will release the trunk as commonly known in the' art.

v,Since the above described testing circuits 'use direct current connections between the remotely controlled oce and the other office arranged for tandem testing a` maximum 1500 ohms loop resistance is required which means that rsuch other oces must be within a limited distance from the vremotely controlled oice.

What is claimed is: y

1.v A remotetesting system for performing telephone subscriber direct current loop test comprising a test station, a remotelylocated oce, means for establishing a test path to said remote oice and for generating alternating current control signals for transmission over said path to said remote oliice,l means at ysaid remote office for translatingsaid .controlsignals into directcurrent loop tests, means ,for translating thev test results intoalternat# ing" current signals forv transmission over said path to the test station, a plurality of other oflices located within a limiteddistance from said remotely controlled oice, and

1. means under the control of said -test station'for testing said other'ofiices 'over a :direct'l current trunkfbetweensaid remotely 'controlled'olilce' and eaclifof saidrothe'r oflices.

2. A remote testing system as defined in claim 1 comprising a plurality of'ke'ys 4at saidrtest :station and a plu-' rality of corresponding relays at said remotely controlled oflic'e res'por'isive to the operation' of rsaid keys to connect said remotely controlled oice to said direct current trunk for performing direct -current loop testsv atl said other 3; A remote testing system as defined in claim 2 further including means at said remotely controlled oce under 5 6 ing various direct current loop tests to said other oices. in the maximum loop resistance of said direct current 4. A remote testing system as dened in claim 3 intrunk is 1500 ohms. cluding a supervisory circuit comprising a number of relays connected in series and wherein said means for References Cited applying supervisory signals to said direct current trunk 5 UNITED STATES PATENTS comprises means for varying the direct current loop reones of said relays to connect various test trunks having access to the subscriber loops to be tested. RATHLEEN CLAFFY Primary Exammer 5. A remote testing system as defined in claim 4 where- D. W. OLMS, Assistant Examiner 

